The present invention relates to disposable, biopotential electrodes.
Certain physiological phenomena of the body produce electrical potentials on the skin. The electrical data associated with the physiological functioning of the heart typifies such potentials. The electrical activity of the brain is another example. In order to obtain such data, it is necessary to attach electrodes to the skin of the patient. A plurality of electrodes are usually employed to measure electric potentials between a number of points on the body.
In the past, belts, or more commonly, suction bulbs were used to hold electrodes, such as electrocardiographic electrodes, on the skin. Belts are awkward to use. An electrolytic paste must be used with suction electrodes to improve the electrical connection and the suction seal. The reuse of such electrodes presents a possiblity for the transmission of disease.
As a result, disposable electrodes have been developed. An early type of disposable electrode was in the form of an adhesive pad with the male portion of a snap fastener extending through the center of the pad. A sponge, saturated with electrolyte, was placed over the fastener. A carrier covered the pad and sponge.
In use, the carrier was removed and the electrode applied to the skin with the adhesive pad holding the electrode on the skin. The lead cables for the electrocardiograph contained a mating part of the snap fastener for connection purposes. After use, the electrode was removed from the skin and discarded.
U.S. Pat. Nos. 3,834,373; 3,923,042; 3,976,055; and 3,993,049 generally show electrodes of this type.
While possessign advantages over suction electrodes, electrodes of the above described type were relatively expensive for a disposable product. Additionally, the electrolyte tended to dry out during storage, limiting the shelf life of the product.
Further development of disposable electrodes has resulted in those generally formed with a foil or film-like electrical conductor having various electrolytic and adhesive layers laminated thereon. A plastic backing sheet may be used to support the foil or film conductor. A connector extending from the foil or film is used to connect the electrode to the electrocardiograph. See, for example U.S. Pat. No. 4,125,110 to Hymes. See also U.S. Pat. Nos. 4,365,634 to Ober, et al; 4,524,087 to Engel; and 4,543,958.
However, the construction of these electrodes is such that they have difficulty in complying with all standards established by governmental regulation or industry groups for such electrodes. These standards contain certain specifications for the electrical properties of such electrodes including DC offset, AC impedance, electrical noise, bias tolerance, and defibrillation recovery. The current specification for the defibrillation recovery characteristics of a disposable electrode, as promulgated by the Association for the Advancement of Medical Instrumentation, is both important and difficult for existing electrodes of the foregoing type to meet. The specification describes certain time related, electrical dissipation properties of the electrode following the repeated electrical shock of defibrillation. If recovery time is not sufficiently quick, there will be an inordinate delay in obtaining electrocardiographic data following defibrillation. The absence of such data can be detrimental to the patient. The specification also limits the voltage that can appear on the electrode immediately following defibrillation, as well as the resultant change in voltage on the electrode over time as the electrode depolarizes.
Additionally, the cost of electrodes of this type has been greater than that desired for a disposable device.